Hydrocarbon wax coatings and their process of preparation



United States Patent 3,503,770 HYDROCARBON WAX COATINGS AND THEIRPROCESS OF PREPARATION James E. Guillet, Toronto, Ontario, Canada, andHarry W. Coover, Jr., Kingsport', Tenn., assignors to Eastman KodakCompany, Rochester, N.Y., a corporation of New Jersey No Drawing.Continuation of application Ser. No. 309,391, Sept. 17, 1963. Thisapplication Aug. 7, 1967, Ser. No. 658,946 The portion of the term ofthe patent subsequent to Oct. 8, 1980, has been disclaimed and dedicatedto the Public Int. Cl. C08h 9/00 US. Cl. 106270 11 Claims ABSTRACT OFTHE DISCLOSURE Hydrocarbon waxes capable of forming wax coatedsubstrates. These waxes have improved tack time and find particular usein curtain coating operations.

This application is a continuation of application Ser. No. 309,391 filedSept. 17, 1963, which is a continuationin-part application Ser. No.79,872 filed Dec. 30, 1960, now U.S. Patent 3,106,485 issued Oct. 8,1963.

This invention relates to hydrocarbon wax coated sub strates and theirprocess of preparation. More particularly, this invention relates tosubstrates coated with a synthetic wax which exhibits a substantiallyimproved tack time in comparison to prior art waxes. In a specificaspect, this invention relates to substrates coated with butene polymerwaxes and a process for preparing the same.

For a number of years, various substrates, including paper, metal foil,fabrics, foodstuffs and the like, have been coated with synthetic waxesprepared from a-monoolefins such as butene to preserve and protect thecoated surface. In recent years, melt coating procedures, such ascurtain coating, have been employed to coat various substrates,particularly those of irregular shape. In this method, the substrate tobe coated is passed through a curtain of molten wax which is provided bya spray head or other suitable means. The wax curtain, except whenbroken by the passage through it of a substrate, falls directly into acollector and is returned to a molten wax reservoir for reuse. Where asubstrate to be coated is regular in shape such as paper, fabric or thelike, the wax is generally applied to the substrate using a gravure rollimmersed in a fountain containing the molten wax or it can be appliedfrom a slit die onto the surface and smoothed with a doctor blade. Thecoated substrate can then be taken up on a rewind roll. Where thesubstrate has an irregular contour, for example, ham, bacon, nuts,bolts, or the like, it is curtain coated by placing it on a moving beltor roller and passing it rapidly through a curtain of molten wax. Themolten wax is cooled substantially simultaneously upon contact with thesolid substrate which is usually at a temperature below the meltingpoint of the wax.

The prior art synthetic wax coatings prepared by the above melt coatingtechniques often exhibit gOOd physical properties including good clarityand sparkle, tensile strength and toughness. However, these coatings aretacky for periods of about 120 to about 135 seconds which is much toolong for commercial coating operations. During the period when the waxcoating is tacky, hereinafter referred to as tack time, coatedsubstrates will adhere to one another and to surrounding materials whichgives rise to problems in handling these materials and often damages thecoating. Furthermore, substrates such as paper are generally melt coatedin commercial operations at high rates, for example, rates of 200 feetper minute and generally rates in excess of 500 feet per minute so thatsuch a prolonged tack time requires slower rates or additional equipmentsuch as conveyors and rollers to run the coating in air until it becomessubstantially free of tack. For most melt coating commercial operationstack times no greater than about 45 seconds can be tolerated without anysubstantial delay in processing.

It is evident, therefore, that the state of the art will be greatlyenhanced by providing synthetic wax coatings which have tack times whichdo not exceed about 45 seconds and often are not in excess of 30seconds. Likewise, a significant contribution to the art would besubstrates coated with such materials and a process for theirpreparation.

Accordingly, it is an object of this invention to provide synthetic waxcoatings exhibiting improved properties.

Another object of this invention is to provide coated substrates whichexhibit improved tack times.

Another object of this invention is to provide synthetic wax coatingswhich can be applied by melt coating techniques, particularly curtaincoating procedures, to substrates without exhibiting the poor tack timescharacteristic of prior art synthetic wax coatings available heretofore.

Still another object of this invention is to provide a method forobtaining the aforementioned improved synthetic wax coatings and coatedsubstrates.

Other objects and advantages of this invention will become apparent froman examination of the specification and claims that follow.

It has now been found that a particular type of hydrocarbon wax, ashereinafter described, when contacted at a temperature up to about 180C., in the molten amorphous state, with a substrate to form a filmhaving a thickness no greater than about 60 mils will crystallize andform a coating having a tack time no greater than about 45 seconds andgenerally no greater than about 30 seconds. In order to obtain theseresults the synthetic wax must be a hydrocarbon polymer of anu-monoolefin containing at least 4 carbon atoms, have a density in therange of about .83 to about .94, an inherent viscosity in Tetralin at145 C. in the range of about .2 to about .5, a melt viscosity at 190 C.in the range of about 1,500 to about 20,000 cp., a brittle point nolower than about C. and be able to crystallize at a temperature at least40 C. below its D.T.A. melting point within about 5 to about 45 secondsafter contact with the substrate upon which it is coated.

The discovery that the aforementioned synthetic waxes would formsubstantially tack-free coatings in 45 seconds or less was quitesurprising and could not have been predicted from the prior art. Thus,it is known that hydrocarbon waxes can be made by thermal degradation ofhigh-molecular-weight polyolefins such as polypropylene and polyethyleneas shown by British Patent No. 569,043 and US. Patent No. 2,835,659,respectively. However, these hydrocarbon waxes are hard, brittlematerials with melt viscosities ranging from about 50,000 to about 30cp. at 190 C. and when coated on substrates, particularly paper or foilin thin layers, form brittle coatings which are substantially free oftack but crack when flexed. Furthermore, hydrocarbon polymers ofa-monoolefins containing at least 4 carbon atoms, unless they have theproperties set forth hereinabove, form coatings which exhibit tack timesof the order of -135 seconds. It was completely unexpected, therefore,that polymers prepared from these same monomers, but have the specificproperties set forth above, would form coatings that have tack timeswhich do not exceed about 45 seconds and generally are of the order ofabout 30 seconds, or less.

In practicing this invention, the hydrocarbon waxes in the moltenamorphous state are contacted with the substrate to be coated attemperatures up to about 180 C. In general, coating temperatures in therange of about to about 150 C. are employed, although it is desirable tooperate at temperatures of about 20 C. It should be understood, however,that the most desirable results will be achieved at coating temperatureswhich will vary with the nature and composition of the particularhydrocarbon wax within the limits set forth. Temperatures substantiallyin excess of about 180 C. are not satisfactory because the prolongedheating employed in melt-coating operations can cause excessiveoxidation of the synthetic wax which deleteriously affects the coating.Furthermore, if the substrate to be coated is bacon or some foodstuff,temperatures above about 180 C. generally results in cooking thematerial which obviously should be avoided. At temperatures up to about180 C., the wax is formed into a film having a thickness not greaterthan about 60 mils. In general, the film thickness will be in the rangeof about 1 to 10 mils, although film thickness of less than 1 mil can beprepared in practicing this invention. If the hydrocarbon wax is coatedin a film having a thickness in excess of 60 mils the coating exhibits atack time well in excess of 45 seconds, for example, tack times of 100or even 130 seconds.

The hydrocarbon waxes are in the molten amorphous state when contactedwith the substrate to be coated, for example, paper, glass, wood, ham,bacon, nuts, bolts, and the like. It is obvious, therefore, that the waxemployed must be one having a melting point no greater than about 180 C.Upon contact with the substrate, which is below the melting point of thewax, the amorphous polymer cools below its melting point and is allowedto crystallize to form a coating which is substantially tack free in 45seconds or less. In order to achieve this result, the hydrocarbon Waxmust be able to crystallize at a temperature at least 40 C. below itsD.T.A. melting point within about 5 to about 45 seconds after contactwith the substrate upon which it is coated. Generally, the hydrocarbonwax employed will be capable of crystallizing at a temperature in therange of about 50 to about 125 C. below the D.T.A. melting point of thewax. Furthermore, the wax must be able to crystallize at thesetemperatures within about 5 to about 45 seconds, preferably about 5 to30 seconds, after contact with the sub strate, which is at a temperaturewithin the above ranges The crystallizability of the Wax can be shown byX-ray or infrared analysis, as is obvious to those skilled in the art.The D.T.A. melting point is determined by differential thermal analysis(D.T.A.) and, is reported in C. This method has been used extensivelyfor determining polymer melting points and is described in detail inOrganic Analysis, vol. 4, Interscience Publishing Co. (1960), page 361.Certain hydrocarbon waxes will exhibit two D.T.A. melting peaks, as, forexample, hydrocarbon waxes that contain stereo-regular blocks of twodifferent polymerized u-monoolefins. The D.T.A. melting point which isreferred to hereinabove is the highest of two D.T.A. melting pointswhere a particular polymer wax exhibits two such melting points.

It has been found that synthetic hydrocarbon waxes having the propertiesset forth above can be melt coated according to the process of thisinvention and will form coatings that are tack free in 45 seconds orless and exhibit other god physical characteristics. Any low molecularweight hydrocarbon polymer of an a-olefin containing at least 4 carbonatoms having a density in a range of about 0.83 to about 0.94,preferably about 0.88 to about 0.93, an inherent viscosity in the rangeof about .2 to about .5, preferably about .25 to about .4, in Tetralinat 145 C., a melt viscosity in the range of about 1,500 to about 20,000cp., preferably about 5,000 to about 10,000 cp. at 190 C., and brittlepoints no lower than about 80 0., preferably in the range of about toabout 60 C., can be employed in the process of this invention if theywill crystallize as described hereinbefore. Although any of theaforementioned waxes can be employed in the process of the invention, itis preferred that the waxes be low molecular weight hydrocarbon homo orcopolymers of one of the well-known polymerizable aliphatic a-olefinscontaining 4-10 carbon atoms. When copolymers of a-olefins are employedin the process of this invention, it is generally most desirable to usecopolymers containing at least 40%, and more preferably about 40-45%, byweight, of one of the aliphatic a-olefins containing 4-6 atoms, thepreferred being butene. In addition, copolymers of a-olefins containingat least 4 carbon atoms with a lower aliphatic a-olefin such aspropylene, should usually contain no more than about 60%, preferably nomore than about 40 to 50%, by weight, of the propylene for best results.The ot-olefins that are used to form the hydrocarbon waxes employed inthe process of this invention can be generally described as having theformula CH;, :CH-R where R is an alkyl radical containing at least 2carbon atoms. Examples of the a-olefins include butene,4-methyl-1-pentene, 4-methyl-1-hexene, S-methyl-l-hexene,4,4-dimethyl-l-pentene, 3-methyl-lbutene, pentene, hexene, octene,decene, and the like.

The physical properties exhibited by the hydrocarbon waxes employed inthe process of this invention can be determined using any of theprocedures generally employed for this purpose. For example, the meltviscosity can be determined using a standard Brookfield viscometer or aCapillary Melt Method. The inherent viscosity of the hydrocarbon waxesemployed can be determined in Tetralin at C., a typical procedure beingdescribed by Schulken et al. in The Journal Of Polymer Science, volume26, page 227 (1957) and the brittle point can be determined using theprocedure described in ASTM D 746-57T employing a sample which is in theorder of 5 to 10 mils in thickness. As already indicated, a wax will besuitable in most commercial melt coating applications if it forms acoating having a tack time that is no greater than about 45 seconds,preferably below 30 seconds. Tack time is that period when a syntheticwax coating is tacky or sticky to the touch and tends to adhere to othermaterials. A simple test for establishing the tack time of a wax coatingis merely to touch the coating with the finger. If the coating tends toadhere to the finger upon touching after a period of 45 seconds it isnot suitable for most commercial operations.

In practicing this invention, any of the conventional methods of meltcoating can be employed. For example, the hydrocarbon wax can be appliedto the substrate using a gravure roll immersed in a fountain containingthe molten wax or it can be applied from a slit die onto the surface ofthe substrate and smoothed with a doctor blade. The wax coating can alsobe applied using the curtain coating technique which is particularlyadvantageous where the substrate to be coated is of irregular form.Furthermore, this method provides a simple, direct, and economicalmethod for packaging irregularly shaped articles which are extremelydifficult to package in other ways. A wax coating prepared according tothe process of this invention using curtain coating adheres to an objectand follows the contour of irregularly shaped articles to form clearcoatings with improved tack times. In addition, if articles to be coatedare placed upon a support and both support and article are passedthrough the curtain of molten wax this results in an attractive packagein which the wax coating adheres to the article and secures it to thesupport. Such packages are particularly attractive because the coatingsdo not bridge or balloon from the article to the support but rather,follow the contour of the article and support. Using this method, it ispossible, therefore, to package such irregularly shaped articles, asnuts, bolts, screw drivers, ham

slices and bacon slices in an attractive manner. The most significantaspect of this invention is that the hydrocarbon wax coating is preparedfrom a wax having the particular characteristics set forth in detailherein. When such a wax is contacted with a substrate, at least 40 C.below the D.T.A. melting point of the wax, it cools and crystallizes toform a substantially tack free coating in about 5 to about 45 seconds.

In general, the process of this invention can be used to coat anysubstrate and the coating can be applied to one or more sides of thesubstrate. In addition to coating paper for packaging as abovedescribed, this invention can be used in coating substrates such asfoil, glass, fabric, wood, ham, bacon, bologna, nuts, bolts, screwdrivers, pliers, and the like.

This invention can be further illustrated by the following examples ofpreferred embodiments thereof although it will be understood that theseexamples are included merely for purposes of illustration and are notintended to limit the scope of the invention unless otherwisespecifically indicated.

EXAMPLE 1 The novel polymer waxes of this invention are particularlyvaluable coating materials and can be coated on a number of substratessuch as paper, foil, food, etc. A particularly etfective method for thispurpose is to employ a curtain coater. To illustrate, 50 lbs. of apropylene l-butene copolymer wax containing approximately 40%, byweight, l-butene is charged to the reservoir of a machine designed forcurtain coating. Said wax has a density of 0.90, an inherent viscosityof 0.4 in Tetralin at 145 C., a melt viscosity of 9,000 cp. at 190 C.and is able to crystallize at a temperature at least 40 C. below its DTAmelting point within 5 to about 45 seconds. The polymer wax is melted inthe reservoir and raised to a temperature of 175 C. It is then pumpedthr ugh a spray-head which gives a curtain of molten wax approximately12 in. wide and 5 mils in thickness. The wax curtain falls directly intoa collector and is returned to the melt reservoir except when an objectis passed through the curtain. Objects to be coated are placed on movingbelts or rollers and passed rapidly through the curtain. The melt iscooled substantially simultaneously upon contact with the solid objectwhich is at a temperature of about 120 C. below the DTA melting point ofthe wax. Coatings on bacon placed on a support are made by the followingprocedure:

A piece of paper board approximately 6" x 12" is passed through thecurtain of molten wax, as described above. This results in a thin,uniform coating of the wax on the paper surface. One-half pound ofsliced bacon is then placed on the coated surface of the board andpassed through the curtain. This results in a smooth, tough, transparentcoating which completely encloses the bacon. After cooling, the coatingcan be removed from the package by peeling it away from the bacon in asingle continuous film. The resulting coating having a thickness ofabout 5 mils shows a tack time of 19 seconds and a brittlenesstemperature of 38.5 C.

When the melt temperature of the hydrocarbon wax is raised to 185 C. theraw bacon coated with the wax is undesirably discolored due to scorchingor cooking. In addition, excessive degradation of the wax occurs duringcontinuous coating operations resulting in a severe loss of filmtoughness.

EXAMPLE 2 The procedure of Example 1 is followed except that thehydrocarbon wax is a copolymer of propylene and l-butene containingapproximately 50% by weight 1- butene, and having a density of 0.885, aninherent viscosity of 0.45 in Tetralin at 145 C., and a melt viscosityof 11,500 cp. at 190 C. The resulting coating shows a tack time of 30seconds and a brittleness temperature of 32 C.

When a similar propylene butene copolymer wax, but having a meltviscosity of 23,000 cp. at 190 C. is substituted in the above procedure,the temperature for coating must be increased to above 180 C. and thereis obtained a coating which exhibits a tack time substantially in excessof the desired 45 seconds.

EXAMPLE 3 A propylene l-butene copolymer wax containing approximately45% l-butene by weight and having a density of 0.89, an inherentviscosity of 0.38 and a melt viscosity of 8,700 cp. at 190 C. is melted,placed in the reservoir of a single-roll kiss-coater for hot-meltcoating operations and maintained at a temperature of 180 C. A roll of40-pound bleached kraft paper is coated with the wax to a depth of 1 milat a speed of 65 feet per minute. The resulting coating shows a tacktime of 12 seconds.

When a propylene l-butene copolymer wax which is unable to crystallizeat a temperaure of at least 40 C. below its D.T.A. melting point within45 seconds is used in the kiss-coating operation, the resulting waxcoating has a tack time in excess of 45 seconds and the coatingoperation must be carried out at prohibitively low rates to prevent thecoated paper from sticking together in the roll. At the very highcoating rates necessary in commercial operations this is, of course, asignificant disadvantage. To illustrate, a propylene l-butene copolymerwax containing 65% l-butene, by weight, and showing a brittlenesstemperature of C. in the form of an oriented, quenched film of 5 milsthickness, gives a wax coating having a tack time of seconds. Similarresults are obtained when the above procedure is used to prepare a filmhaving a thickness in excess of 60 mils.

EXAMPLE 4 The procedure of Example 1 is followed using a propylenel-hexene copolymer Wax containing 35% l-hexene by weight, having adensity of 0.88, an inherent viscosity of 0.45 in Tetralin at C., a meltviscosity of 12,000 cp. at 190 C. and a brittle point of 25 C., andbeing able to crystallize at a temperature 65 C. below its D.T.A.melting point within 30 seconds. The resulting wax coating shows a tacktime of less than 15 seconds.

Similar results are obtained when the above hydrocarbon wax is replacedwith a propylene l-octene copolymer wax containing 40% l-octene, byweight, and having a melt viscosity of 3,500 cp. at 190 C., an inherentviscosity of 0.30 and a brittle point of 36 C.

EXAMPLE 5 The procedure of Example 1 is followed using a propylenel-decene copolymer containing 33%, by weight, 1- decene and having aninherent viscosity in Tetralin at 145 C. of 0.38, a melt viscosity of5,300 cp. at 190 C., and a brittle point of 60 C. The resulting waxcoating has a tack time of 12 seconds.

When propylene l-decene copolymer wax containing about 50% l-decene byweight and having a melt viscosity of 11,500 cp. at 190 C., and abrittle point of about 87 C. is used in the coating operation in placeof the above hydrocarbon wax, the resulting wax coating has a tack timeof 90 seconds. This tack time is too long for commercial operations,since coated packages on an assembly line tend to stick together andcannot be processed satisfactorily.

EXAMPLE 6 The results obtained with a hydrocarbon Wax which does notcrystallize within 5 to 45 seconds at a temperature at least 40 C. belowits D.T.A. melting point are highly unsatisfactory. To illustrate, al-butene l-hexene copolymer containing 20% l-hexene and having a meltviscosity of 1,800 cp. at 190 C. and an inherent viscosity of about 0.2is coated onto cold bacon using a curtain coater. The resulting coatinghas a tack time of greater than seconds. A sample of the above l-butene1-hexene copolymer, when melted and cooled rapidly to 7 80 C. below itsD.T.A. melting point, will not crystallize within 45 seconds aftercooling.

Thus, by means of this invention there is provided novel hydrocarbon waxcoatings exhibiting excellent physical properties including asubstantially reduced tack time in comparison to hydrocarbon wax coatingnow available. Substrates coated according to the process of thisinvention can be used in packaging food, dry goods and other articleswhich require protection from moisture or air.

Although the invention has been described in considerable detail withreference to certain preferred embodiments thereof, it will beunderstood that variety and modifications can be effected withoutdeparting from the spirit and scope of the invention as describedhereinabove and as designed in the appended claims.

We claim:

1. The method of providing an improved wax coating which comprisescontacting, at a temperature up to about 180 C., a synthetic wax in themolten amorphous state, with a substrate to form a film having athickness no greater than about 60 mils, said synthetic wax being ahydrocarbon polymer of an a-monoolefin containing at least 4 carbonatoms having a density in the range of about .83 to about .94, aninherent viscosity in Tetnalin at 145 C. in the range of about .2 toabout .5, a melt viscosity at 190 C. in the range of about 1,500 toabout 20,000 cp., a brittle point no lower than about -80 C. and beingable to crystallize at a temperature at least 40 C. below its D.T.A.melting point within about to about 45 seconds after contacting saidsubstrate.

2. The method of claim 1 in which the synthetic wax is a hydrocarbonpolymer of an a-monoolefin containing 4 to carbon atoms.

3. The method of claim 1 in which the synthetic wax is a hydrocarboncopolymer of an ot-monoolefin containing 4 to 10 carbon atoms.

4. The method of providing an improved wax coating which comprisescontacting, at a temperature in the range of about 0 toiabout 150 C., asynthetic wax in the molten amorphous state, with a substrate to form afilm having a thickness in the range of about 1 to about 10 mils, saidsynthetic wax being a hydrocarbon polymer of an a-monoolefin containingat least 4 carbon atoms, having a density in the range of about .88 toabout .93, an inherent viscosity in Tetralin at 145 C. in the range ofabout .25 to about .4, a melt viscosity at 190 C. in the range of about5,000 to about 10,000 cp., a brittle point in the range of about l0 toabout 60 C. and being able to crystallize at a temperature in the rangeof about 50 to about 125 C. below its D.T.A. melting point within about5 to about 30 seconds after contacting said substrate.

5. The method of claim 4 in which the synthetic wax is a butenepropylene copolymer containing about 40 to about 45%, by weight, ofbutene.

6. The method of claim 5 in which the substrate is bacon.

7. The method of claim 5 in which the substrate is ham.

8. The method of providing an improved wax coating which comprisescontacting, at a temperature of about 175 C., a synthetic wax in themolten amorphous state, with a substrate, to form a film having athickness of about 5 mils, said synthetic wax being a propylene lbutenecopolymer containing about 40%, by weight, of l-butene, having a densityof about .90, an inherent viscosity in Tetralin at C. of about .4, amelt viscosity at 190 C. of about 9,000 cp., a brittle point of about38.5 C. and being able to crystallize at a temperature at least 40 C.below its D.T.A. melting point within about 5 to about 45 seconds aftercontacting said substrate.

9. The method of providing an improved wax coating which comprisescontacting, at a temperature of about C., a synthetic wax in the moltenamorphous state, with a substrate, to form a film having a thickness ofabout 5 mils, said synthetic wax being a propylene 1- hexene copolymercontaining about 35% by weight, of l-hexene, having a density of about.88, an inherent viscosity in Tetralin at 145 C. of about .45, a meltviscosity at C. of about 10,000 cp., a brittle point of about 25 C. andbeing able to crystallize at a temperature of about 65 C. below itsD.T.A. melting point within about 30 seconds after contacting saidsubstrate.

10. The method of claim 4 in which the synthetic wax is a propylenedecene copolymer containing about 33%, by weight, l-decene having aninherent viscosity in Tetralin at 145 C. of .38, a melt viscosity ofabout 5,300 cp. at 190 C. and a brittle point of about 60 C.

11. The product obtained by the process according to claim 1.

References Cited UNITED STATES PATENTS 3,243,395 3/1966 Guillet et a126028.5

JULIUS FROME, Primary Examiner JOAN B. EVANS, Assistant Examiner US. Cl.X.R.

99l69; 106271, 285; 1l7-l4l; 26033.6, 93.7

